Vesicoureteric reflux (retrograde passage of urine from the bladder into the ureter) can be secondary to bladder outlet obstruction or to a neuropathic bladder. However, most occurrences are due to a primary anatomical defect in the junction of the ureter and the bladder. Primary vesicoureteric reflux is usually found during investigation of urinary tract infection in children, but screening shows that it is present in 1-2% of symptom-free children. Moreover, it is often inherited in an autosomal dominant manner, making it one of the commonest of inherited disorders. Mutations of a transcription factor gene which controls prenatal development of the kidney and urinary tract have been found in a rare syndrome which includes vesicoureteric reflux. Vesicoureteric reflux is associated with pyelonephritis, renal scarring, hypertension and renal failure and these associations may be prevented by medical treatment. Early screening for this reflux is recommended in families with other affected members.